1. Technical Field
The present invention relates to thermowelding, and more particularly to a technique for thermally welding edges of a battery module.
2. Related Art
A battery stack to be disposed in a vehicle is constructed by means of arranging (stacking) a plurality of battery modules—which are formed from nickel-metal hydride batteries of one type or from a plurality of cells—in parallel to each other with cooling passages laid among the battery modules; assembling the battery modules by means of constraining edge members placed at the two ends of the modules; and electrically interconnecting the battery modules in series. Edges of each of the battery modules are sealed by means of thermally welding a resin portion of a module main body and a resin case for sealing purpose (hereinafter called a “sealing resin case”), and an outlet used for discharging a hydrogen gas to the outside and terminals are caused to protrude from the case.
A thermowelding apparatus equipped with a heater is used for thermowelding. FIG. 4 shows a perspective external view of a related-art thermowelding apparatus. Further, FIG. 5 shows an enlarged view of the heater shown in FIG. 4.
A thermowelding apparatus 1 has a flat heater 10, a holder 12 for holding this heater 10, and terminal units 14 for heating the heater 10. The heater 10 is spanned between the terminal units 14, and the terminal units 14 are connected to a heat source. The heater 10 is formed from a nichrome wire or the like. When the heater 10 is heated and the thermowelding apparatus 1 is brought into contact with a substance to be thermally welded, such as a battery module, the heater 10 adheres to the surface of the substance, thereby posing difficulty in removal of the heater. In light of the difficulty, the heater 10 is brought into contact with the substance to be thermally welded while ease of peeling is ensured by means of placing a Teflon (Registered Trade Name) tape 16 between the heater and the substance, thereby thermally welding the substance. As shown in FIG. 5, the heater 10 is formed from a heater main body 10a and terminal sections 10b. The flat-plate-shaped heater main body 10a is brought into contact with a plane to be thermally welded, by way of the Teflon tape 16.
2000-169797 A describes a technique intended for preventing infliction of damage to a releasable tape, which would otherwise be caused by a difference between a coefficient of thermal expansion of a plate-like heater and a coefficient of thermal expansion of the releasable tape. To this end, according to the technique, a thermally-adhesive sheet is positioned between a pressure bed, and a plate-like heater located opposite the pressure bed, the plate-like heater being provided with, in a non-contacting manner, a releasable film of a releasable tape made from a material exhibiting releasability. The plate-like heater and the pressure bed are moved mutually in a closing direction, and the thermally-adhesive sheet is subjected to pressurization and heating, thereby sealing the thermally-adhesive sheet.
Moreover, 2006-40694 A describes a configuration intended for providing a hermetic battery which enables easy sealing of a battery housing and in which the battery housing exhibits superior thermal conductivity. As shown in FIG. 6, the hermetic battery has a power-generating element 140 including a positive electrode and a negative electrode; and a battery housing 110 for housing the power-generating element. The battery housing 110 comprises a first housing member 111 which is made of metal and whose inner side surface is exposed within the housing; a second housing member 116 which is made of metal and whose interior surface is exposed within the housing; a first resin member 121 which is made of resin and fixed to the first housing member 111 in a fluid-tight manner; and a second resin member 126 which is made of resin and fixed to the second housing member in a fluid-tight manner. The first resin member 121 and the second resin member 126 are thermally welded together, thereby sealing the battery housing 110.
WO 2006/013743A1 describes the configuration of another battery module and a coating method involving interposition of a sealing member. FIG. 7 shows the configuration of this related-art battery module. A battery module 300 essentially assumes the shape of an rectangular parallelepiped comprising mutually-opposing first and second long side surfaces 300a and 300b, mutually-opposing first and second short side surfaces 300c and 300d, and mutually-opposing first and second end faces 300e and 300f. The battery module 300 comprises a cell group 310 consisting of a plurality of cells 311; a gas duct member 330 for covering respective safety valves of the cell group 310; a positive side cover 340 and a negative side cover 350 for covering the cell group 310 and the gas duct member 330 from both ends thereof along a direction in which the cells are to be aligned in a row; and a sealing member 360 for hermetically sealing the entire module by enveloping the cell group 310 and the gas duct member 330. FIG. 8 shows a sheet-shaped sealing member 461 as an example of the sealing member 360. The sheet-shaped sealing member 461 assumes a rectangular shape consisting of mutually-opposing first and second sides 461a and 461b and mutually-opposing third and fourth sides 461c and 461d. An adhesive is applied, along the first side 461a, to a strip-shaped first side edge section 463 placed on the upper surface of the gas duct member 330. Meanwhile, a second non-adhesive area 465h—which extends from the third side 461c to the fourth side 461d and is not thermal-sprayed with an adhesive—is formed in a strip-shaped second side edge section 465 which is placed on the upper surface of the gas duct member 330 along the second side 461b and which overlaps the first side edge section 463 from the outside. A strip-shaped second adhesive area 466 thermal-sprayed with an adhesive is formed along an area closer to the second side 461b than to the second non-adhesive area 465h in the second side edge section 465. A third non-adhesive area 467h—which extends from the first side 461a to the second side 461b and which is not thermal-sprayed with an adhesive—is formed, along the third side 461c, in a strip-shaped third side edge section 467 which runs around the positive side cover member 340 and is to be fixed thereto. A fourth non-adhesive area 469h—which extends from the first side 461a to the second side 461b and which is not thermal-sprayed with an adhesive—is formed, along the fourth side 461d, in a strip-shaped fourth side edge section 469 which runs around the negative side cover member 350 and is to be fixed thereto. This sheet-shaped sealing member 461 is wrapped around the battery module 300 having not yet been sealed so as to cause the second side edge section 465 to overlap the first side edge section 463. The side edge sections are hermetically fixed into a cylindrical shape by means of welding. Namely, the second non-adhesive area 465h—which is not thermal-sprayed with an adhesive—in the second side edge section 465 is superimposed on the first side edge section 463 from the outside and fixed through welding without interposition of an adhesive. The third side edge section 467 constitutes one opening end section and encloses the positive side cover member 340 and is hermetically fixed to the positive side cover member 340 through welding without interposition of an adhesive. The fourth side edge section 469 constitutes the other opening end section; encloses the negative side cover member 350; and is hermetically fixed to the negative side cover member 350 through welding.
However, under the method for bringing the heater 10 into contact with a surface to be welded by way of the Teflon tape 16, warpage arises in the heater 10 during heating operation. In addition, replacement of the Teflon tape 16 is required at every given period, which entails an increase in cost and deteriorated working efficiency. Moreover, thermowelding is performed by way of the Teflon tape 16, and hence there arises a necessity for increasing the heating temperature of the heater 10, and a thermowelding time is also increased. Furthermore, air accumulates between the Teflon tape 16 and the heater 10, and hence the quality of a surface to be welded is degraded.